The present invention relates to a method of discriminating a type of a fuel to be supplied being supplied from a fuel tank of a motor vehicle. More particularly, the present invention relates to a method of discriminating an octane number of a fuel in which the octane number of gasoline being supplied to a gasoline engine is discriminated. In other words, in the present invention, determination is made as to whether the gasoline is of a high-octane or a low-octane gasoline.
It is well known to control an ignition timing at which an ignition plug sparks in accordance with an engine rotational speed and an engine load as well as an occurrence of a knocking of the engine. In this case, when the knocking is detected the ignition timing is retarded or approached the top dead center of crank shaft of the engine.
You can access two kinds of gasolines, i.e., high-octane gasoline and low octane gasoline. In this specification, the term low-octane gasoline means that an octane number of the low-octane gasoline is less than that of high-octane gasoline. On the other hand, two kinds of gasoline engines optimized for high-octane gasoline and low-octane gasoline, respectively, are available for the consumer. It is well known that maximum performance of an engine is achieved when the ignition advance angle is advanced to a critical ignition advance angle relating to the knocking of the engine. In case the ignition advance angle is advanced beyond the critical ignition advance angle, the engine would knock.
It is also well known that the more the octane number of the gasoline gets, the more the critical ignition advance angle can get.
In this connection, the following problems may be raised. In case low-octane gasoline is supplied to a gasoline engine designed suitably for the high-octane gasoline, knocking of the engine would frequently occur since an ignition plug may be ignited at the ignition advance angle more than an optimum or critical ignition advance angle for low-octane gasoline. In case the high-octane gasoline is supplied to a gasoline engine designed for use with low-octane gasoline (referred to as the engine for low-octane gasoline), maximum performance of the engine, which is achieved when the low-octane gasoline is used, may not be expected to be obtainable. This is because that the ignition plug may be ignited at the ignition advance angle which is retarded too much with respect to the critical ignition advance angle. More specifically, by supplying high-octane gasoline in the engine for low-octane gasoline, the ignition advance angle could be advanced to the critical ignition advance angle for the high-octane gasoline so that output torque of the gasoline engine increases and exhaust gas temperature decreases resulting in decrease of a fuel injection rate. However, since the gasoline engine for low-octane gasoline provides the ignition advance angle optimum for low-octane gasoline, no critical ignition advance angle for high-octane gasoline is obtainable. This causes the above-mentioned disadvantage.
In order to obviate these disadvantages, there has been proposed in a Japanese Application laid-open No. 57072/1983 an apparatus for controlling an ignition timing in which two tables of ignition timings for high and low octane gasoline are prestored and one of the tables is selected by a driver's switching operation of a switch for selecting of the table. Such a switch may be provided on an instrument panel of the motor vehicle. This apparatus, however, is subjected to the following problem. An erroneous switching operation of the switch for selection of the above table causes the same advantages mentioned above. This is because the driver has to determine which one of high and low-octane gasolines is supplied to the engine so that one of the tables of the ignition timing is selected by switching operation of the switch.
Further, there has been proposed in a Japanese Application laid-open No. 122275/85 an apparatus for controlling an ignition timing in which a determination as to the type of the gasoline to be supplied to the engine is carried out in accordance with a knocking condition of the engine. However, the proposed apparatus necessitates an additional ignition advance angle map for discrimination of the type of the gasoline to be supplied together with a well-known ignition advance angle map for general control of the ignition timing based on an engine operational condition. In determining the type of the gasoline being supplied, the ignition advance angle is selected from the additional ignition advance angle map, at first, and then the ignition plug sparks at the ignition advance angle thus selected. Thereafter determination is made as to whether the knocking of the engine takes place or not. If it is determined that the knocking of the engine takes place, it is found that an undesirable gasoline, e.g., low-octane gasoline is used. Such sequential procedures of discrimination of the gasoline requires a relatively longer period of time.
In addition, in case no additional ignition advance angle map is provided, the ignition advance angle for discrimination of the type of the gasoline has to be calculated from the ignition advance angle for general control of the ignition timing based on the engine operational condition.
Furthermore, the ignition timing control proposed in Japanese Application laid-open No. 122275/85 has further problem which will be described below. The above-mentioned discrimination as to the type of the gasoline is adapted to be repeatedly carried out even after such discrimination has been completed once thereby leading wasteful sequential procedures for discrimination of the type of the gasoline. It should be also noted that the proposed apparatus may be subjected to occurrence of the knocking of the engine immediately after the engine operational condition for knocking control is detected in which the ignition timing is retarded in accordance with occurrence of the knocking of the engine.